Dm A24. Hyperinsulinaemia in subjects with im­paired glucose tolerance and Type 2 diabetes. Mohamed-Ali V., Britton M. E., Yudkin J. S. Academic Unit of Diabetes and Endocrinology, Whittington Hospital, Archway Road, London.

Type 2 diabetes is associated with hyperinsulinaemia. Conventional assays have been shown to overestimate insulin levels due to cross-reaction with proinsulin and proinsulin-like molecules. In order to determine if the apparent hyperinsulinaemia is, in part, due to cross-reacting molecules we used an in-house, amplified, end-point enzymoimmunometric assay (lEMA) for specific measurement of human insulin. The assay was sensitive to 2.0 pmoll- 1

with intraassay coefficient of variation (CV) less than 10% and interassay CV less than 15% . Recovery of insulin from spiked plasma was 96% (range 88 to 105%). The assay was used to measure fasting insulin levels in 107 caucasian subjects with no evidence of heart disease (60 normal glucose tolerance, NGT; 17 impaired glucose tolerance, IGT and 28 newly discovered diabetics, DM). There was a stepwise increase in fasting insulin concentrations from NGT to IGT and to DM [median 28 (range 3-179); 54 (16-232), p= 0.003; 82.5 (15-241), p= 0.0001]. Following a 75 g glucose challenge given to non-diabetics, in normal subjects the 2 hr plasma insulin increased by 299% (interquartile range 85-528%) over fasting, while in IGT this increase was 426 (267-811%). In conclusion subjects with IGT and Type 2 diabetes are not insulin deficient in the fasting state, even using specific assays of insulin, suggesting that insulin resistance must contribute to the aetiology of Type 2 diabetes.

A25. MODY is a dominantly inherited disorder of ,9-cell function. Hattersley A. T.a, Cook J. T. E.a, Scanlon p.b, Firth R.b, Burden F.c, Pyke D.d, Watkins P.d, Manley S. E. a, Turner R. ca. aDiabetes Research Laboratories, Radcliffe Infirmary, Oxford. bMater Misericordiae Hospital, Dublin. crhe General Hospital, Leicester. dKings College Hospital, London.

Maturity O nset Diabetes of the Young (MODy) is charac­terized by the diagnosis of Type-2 diabetes before the age of 2S and a dominant inheritance. The pathophysiology of MODY is uncertain. We studied 62 members of 5 large multi­generation MODY pedigrees to determine if there was a single pathophysiology and its relationship to common Type 2 diabetes (diagnosis > 40 yrs, without dominant inheritance). 21 MODY patients were compared wi th 21 Type 2 diabetic patients individually matched for fast ing glucose (7.6: 7.5 mmol), t reatment and gender. Statistical analysis was Paired t and Student f-tests on logged data. The MODY patients had a lower fasting plasma insul in [5.7 (4.6-7.7) median (interquartile range): 13.2 (9.2-14.9) mU 1- 1 p =O.013]. Using HOMA analysis M ODY patients showed reduced 13-cell function [%8 50 (28-67): 69 (40-94) p",,0.005] and increased insulin sensit ivity [%S 59 (43-67): 27 (22- 34) p < 0.001 ]. The marked absence of obesity in th e MODY patients, in part explains the difference in sensitivity. [8MI 22.8 (21.6-24.7): 27.4 (24.5-33.5) kg m- 2, p< 0.001 ]. 41 unaffected subjects f rom the MODY pedigrees showed significant ly better ,8-cell function [% 8125 (113-157): 50.2 (28-69) p=0.005] than the MODY subjects but were not more

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BDA ABSTRACTS insulin sensitive [%S 61 (44-76): 59 (43-67) p=0.02] or less obese [23.7 (22.5-25.3): 22.8 (21 .6-24.7) kg m - 2 p>O.OS]. In the MODY pedigrees f)-cell function but not insulin sensi­tivity allowed differentiation of affected from unaffected. We conclude that MODY results from the dominant inheritance of a single gene affecting f)-cell function.

A26. Acute hyperinsulinaemia causes an in­crease in neuropeptide Y (NPy) concentrations in the hypothalamic arcuate nucleus of the rat. Malabu U. H., Cotton S. J., Kruszynska Y. T.a, McCarthy H. D., McKibbin P. E., Williams G. Department of Medicine, University of Liverpool, PO Box 147, Liverpool and aDepartment of Medicine, Royal Free Hospital, Pond St., London.

NPY, a major hypothalamic peptide, stimulates feeding, illsulin secretion and weight gain when injected intra­hypothalamically. NPY synthesiS in the arcuate nucleus (ARC) and levels in NPY-sensitive hypothalamic regions rise in diabetes and starvation, pOSSibly stimu lated by insulin deficiency. High pharmacological intracerebrovent ricular insul in levels inhibit NPY synthesis in the ARC, but the effects of hyperinsul inaemia have not been studied. We therefore measured regional hypothalamic NPY levels in rats during a hyperinsul inaemic, euglycaemic clamps. Male W istar rats with implanted jugular cannulae, fasted fo r 24 hrs, were infused with insulin (128.2 mU 1-1 at 780 ~I hr- 1 (n = 7) together with variable-rate glucose to maintain euglycaemia (3.9±0.1 mmoll- 1 ), or saline (n=8; glycaemia, 4.0±0.5 mmoll - 1 ), for 2.5 hrs. Insulin levels were 80.2±10.4 mU 1-1 in insulin-infused rats and 16.7±11.7 mU 1- 1

in saline-treated controls (p<0.001). NPY levels were measured by radiOimmunoassay in the ARC and 7 other hypothalamic regions. NPY levels in the ARC were signi­f icantly higher in hyperinsulinaemic than in control rats (4 .BO±1.17 vs 2 .54±0.58fmol~g protein- 1; p<0.001), but comparable with controls in all other regions. Acute physiological hyperinsulinaemia therefore increase NPY levels selectively in the ARC. Insulin may cause NPY accumu­lation in the ARC by blocking its transport to NPY-sensitive areas, consistent with the suggested inhibition by insulin of NPY and the postulated role of insulin as a satiety factor.

A27. Effect of insulin on intracellular pH in cultured myoblasts from insulin-resistant spon­taneously hypertensive rats. Davies J. E., Quinn P. A., Ng L. L. Department of Pharmacology, Clinical Sciences Building, Leicester Royal I nfi rmary, Leicester.

One postulated mode of insulin action in muscle is the elevation of intracellular pH by stimulation of the Na+/H + antiport leading to increased glycolysis. Such an action in the kidney would also lead to Na+ retention. As spontaneously hypertensive rats (SHR) and hypertensive humans are insulin resistant, we studied the in vitro effect of insulin (1 mU ml-1)

on intracellular pH in cultured myoblasts from SHR and normotensive Wi star Kyoto rats (WKY). Insulin led to a progressive fall in intracellular pH of WKY myoblasts (0 min: mean±SD 7.17±0.10; 15 min 7.09±0.14, p<0.007; 30 min 7.062±0.13, p<0.001), resembling the response of normo-

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